1. Field of the Invention
The present invention relates to a coater for applying a liquid or viscid medium to a moving surface (e.g., a fiber material web, applicator roll or backing roll), and, more particularly, to a coater for applying a coating mixture to a moving surface using a coater rod.
2. Description of the Related Art
A coater for applying a liquid or viscid medium (such as sizing) to a moving surface may include a coater rod which is positioned closely adjacent to the moving surface. The coater rod is driven in a rotational manner and the distance between the coater rod and the moving surface during operation determines the thickness of the coating which is applied to the moving surface. Typically, the coater rod is connected to a beam or mounting via a coater rod bed and a blade. The blade is flexible and allows the coater rod to be moved toward and away from the moving surface using known adjustment devices, such as profile adjusting screws and a load tube. The coater rod bed carries the coater rod and allows the coater rod to be rotatably driven therein.
Occasionally, it may be necessary to stop the operation of the coater, such as may occur during a sheet break of the fiber material web. During such periods of inoperation, the coater rod is typically not rotatably driven, but rather is stationary within the coater rod bed. The coater rod bed, being a relatively large mass relative to the coater rod, cools down from the operating temperature at a relatively slow cooling rate. The cooling rate is particularly slow if the coater rod bed is formed from a relatively poor thermally conductive material, such as polyurethane. On the other hand, the coater rod carried by the coater rod bed includes a portion of the periphery adjacent the moving surface which is exposed to both ambient air as well as possibly wash down water. It has been found by the present inventor that the coater rod may thermally distort by bowing away from the coater rod bed during periods of inoperation as a result of the coater rod being against the relatively hot coater rod bed on one side and cooler ambient air on the other side. After the coater is operated following a period of inoperation, the bowed coater rod results in an uneven coating application with a frequency which is dependent upon the rotational frequency of the coater rod. An uneven coating application caused by bowing of the coater rod is not desirable.
What is needed in the art is a coating machine having a coater rod which is not subject to thermal distortions.